https://s0.wp.com/latex.php?latex=%5Cdisplaystyle+4+%5Csum_%7Bi%3D1%7D%5En+%28n+-+i+%2B+1%29+%28n+-+%5Cleft%5Clceil%5Cfrac%7Bi%7D%7B2%7D+%5Cright%5Crceil+%2B+1%29&bg=ffffff&fg=6a6c6e&s=0